border-1px($color)
    position: relative
    &::after
        display: block
        position: absolute
        left: 0
        bottom: 0
        border-top: 1px solid $color
        width: 100%
        content: ' '
bg-image($url)
  background-image: url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image: url($url + "@3x.png")